Qt Designer: Layout stretch property is not restored if changes to layout are undone

To reproduce:

1. create or open an empty UI file
2. add two TextEdits (because TextEdit expand by default)
3. set a vertical layout on the parent
4. set layout stretch to 3,1
5. remove the bottom TextEdit
6. undo the change (ctrl+z)
7. notice that layout stretch wasn't restored for the bottom TextEdit

It's not a critical issue, but it's a quite annoying especially when the change is caused by mistake or a sudden key press.